Process for stabilizing sterile evaporated milk



Patented May 22, 1951 immense EQBLSIIABILIZING STERILE lEVAPQ S D-JY ELIS Samuel Park, Toledo, Ohio, assignor 't o'- W Mallory Ala-Company, Ann Arbor Mich a corporation of Michigan v o ,Draw ng- Application N Membe 4. 4.

" serial 61 131 .4 Claims.

The present invention relates to a process for producing sterile evaporated milk of the proper body or viscosity -without-the necessity of adding stabilizing salts; and this application is a continuation-impart of applicants copending application -Serial No. 471,013, filed January 1, i943, now'abandoned.

Canned evaporated --milk 'must be sterilized to impart keeping qualities; and ithas been conventional practice -'in all evaporated -mill canneriesf-or many years-to can-the evaporated-milk andthen sterilize by-elevating-the temperature pf the-cans-to f rom 240-- to-2 l5- -F. over a period of from'fifteen-tmtwenty-minutes. Serious-dimculties have been encountered becaus e of-thejnstability of evaporated milk under --sterilizing conditions. While the heat stability of milk from diiferentsources and even that from the same cows at --difierent 'periods 'varies widely, a substantial proportion of allcom-mercial milk,--in=the absence of special treatment, "lacks the heatstability necessary -to withstand sterilization -w-ithout-coagulating. Accordingly agreat'deal of etforthas been expended in an attempt-todevise a satisfactory method of imparting :the proper stability'to'evaporated milk. I -he problem is not simply .one of imparting sufiicient stability because excessive heat stability .is also objectionable .as it :results insterile milk lacking :in :body and which'tends tolseparate in the can.

The generally accepted measure of heat stability is the time "during :WhiCh the evaporated milk .can withstand a temperature of 239 'F. Without :coagulating i. Je., forming a =je11 it is well known that if the evaporatedlmilk .hasa heat stabi1ity-ofirom la fewminutesbver the sterilizing time to approximately twice :the sterilizing time, satisfactory body.- can be obtained.

Two :methods have been known for adjusting the heatlstability l of 'millmduring :the process of producing sterile evaporated milk. The first is by thefforewarming of the milk prior-to evaporation. It has been established that the stability-of milk l-may'zbe increased by heating it :to and holding it atelevated temperatures for 'limited times prior to evaporation. "Ingeneral, the higher the forewarming temperature between 200 F. and 300" F., ethelgreater the heat .stability of the sterilizedlproduct. ':'I -o=.allesser-degree stability increases with .the =time of exposure to any given -.temperature. Care must always ibe exercisedin heating milk to avoid imparting la dark color or. a cooked taste. :Ithas "begins-recognized that for :any .given :temperature the. time .of exposure must :be -:1imited:t0 avoid .-zthesesdifliculties,

the maximum permissible time being greater fllQl the lower --t ernperatures than the higher. "Thus, i yb h d t a :t e a rei mm 2 0 to 2-12 for aperiod-up to twenty fiveminutes but can only be held a few seconds at-300 -It has been noted that for each increase in tern.-

perature of 18* -F., the time should be decreased approximately two and one-;ha lf f o1d.

Forewarming, a1one,'has not proven satisfactory-as-a means of imparting proper stability to evaporated milk because of the difiiculty of adjusting the time and-temperature of iorewarming to-th proper values. 'Ihis problem is greatly aggravated by the constantly varying properties of commercial milk, the large volumes which must be handled in commercial canneries and the inherent inflexibility of the equipment used. Thus, onsome occasions iorewarming to approximately 212 F. for {rpm ten -to twenty-five minutes will impart proper stability, but frequently the stability after -such forewarming -i s*-inadquate. Occasionally, m i1k -forewarrned to --temperatures of-230 F. or=highe r-has excessive stability, but in others satisfactory stability is obtained at temperatures as high as 2-35 F. 248 F. for short periods. Consequently, 'it hias longzbeen-the standard praeticeto =forewarmthe millotoa.fixed-temperature and for a fixed-period calculated to avoid over-stabilization (usually from 200 to 21 2 -for ten -to 'twentyjve minutes). As a result, the forewarmed milk irequentlyhas insufiicien't heat stability. The-necessary additional stability then imparted 'to the milk by the addition of water solutions pf so-called ta ili n a ts such a ls i adium h s h t o s um citrat :Da t the a a a qns i the .P Qn riies o th ed ce n rfi aia tanlie ie a d th sub stantial difierences "between nilli {rpm difierep t raph ca ar as i11 amoun of salt equ re varie widely; .andl tie mp9 ,l h la rknawp hemical orph s qa testto determinet eiprqaer moun x ep by len and tr meth ds :11: standard practice in all evaporated milk o e iie o determine the .a e lt afl i een .ed ach d y b adding n ge c ivel rinlqn sieg u n iti s 41 vsalt to salien t n e ll f th re and l ed A ie 733 21 @3 19 i sarel hen de ermine 7 milk, although the usual range is from two to ten ounces.

The use of stabilizing salts is objectionable, not omy because they are adulterants but because their cost is substantial.

Accordingly,.it is the object of the present invention to provide a novel method which is suitable for use in commercial evaporated milk canneries to produce sterile evaporated milk of proper body without the use of stabilizing salts or other adulterants.

In accordance with the present invention, the desired result is achieved by blending suitable proportions of milk which has been intentionally over-stabilized by heat treatment with milk which is lacking in stability, and sterilizing the mixture. This method has the advantage for commercial use that part of the milk processed in a given plant may be subject to the conventional process which produces milk that is under-stabilized. This milk is then mixed with milk which has been intentionally over-stabilized by special heat treatment. The proper proportions of the mixture must be determined from day to day by the above described empirical tests currently used to determine the amount of stabilizing salt required, the only difference being that each sample will have difierent proportions of the two types of milk instead of varying amounts of stabilizing salts. The heat exchanger used for the specially heat-treated portion may also be of a type which heats the milk to a fixed temperature for a fixed time, and this equipment is then run only long enough each day to produce the necessary amount of over-stabilized milk.

The treated and untreated milks may be combined before or after evaporation. Thus, a portion of the incoming milk supply may be overstabilized by heat treatment, and then mixed with the untreated milk and the mixture evaporated and sterilized. This method has the advantage that the higher temperature employed to overstabilize one portion is utilized to speed up the subsequent evaporation of all of the milk; but to make the necessary cut and trial tests, the trial samples must be evaporated.

Alternatively, unstable and over-stabilized portionsmay be evaporated in separate evaporators or inthe same evaporator at different times, and thereafter mixed in the proper proportions and sterilized. a

Asa second alternative, all of the milk may be evaporated together in the conventional manner to produce unstable evaporated milk and thereafter a portion of the evaporated milk subject to the heat treatment to over-stabilize that portion. The two portions are then remixed and sterilized.

',With both of the alternative methods described, thesamples taken for the out and trial tests are taken after evaporation.

' It will be apparent from the foregoing that the times and temperatures for the over-stabilizing heat treatment are a matter of choice based on principles well known to those skilled in the art of preparing sterile evaporated milk. Temperatures as low as 230 F. would beefiective under some circumstances, and temperatures as high as 300 F. may be employed. As is well known, the time of'exposure to any selected temperature must be limited to prevent injury to the milk and, in general, longer times are required at the lower temperatures and vice versa to produce the same results. As a general guide, the milk may be held at 230 F. for about twenty minutes and at 300 F; for from two to fifteen seconds.

In actual practice, the availability and cost of equipment and other practical considerations may govern the selection of a combination of time and temperature for the treatment used to over-stabilize the milk. This may in some cases result in the choice of temperatures in the lower portion of the range and relatively long times of exposure. However, it is preferred to employ heat treatment at temperatures in the order of from 250 F. for a maximum period of about three to four minutes to 300 F. for a period of about one to two seconds for the portion of the milk which is over-stabilized, since that practice insures substantial over-stabilization of practically all types of milk which will be encountered in a commercial cannery and thus reduces the ratio of the heat-treated portion to the untreated or unstable milk in the final mixture. The remaining or untreated portion of the milk may have the usual treatment conventionally employed in evaporated milk canneries, or may even be subject to higher forewarming temperatures than the usual maximum of 212 F. so long as care is exercised that it is not over-stabilized.

Depending upon the character of the milk supply and the processes to which the two portions of the milk are subject, the amount of heat-treated over-stabilized milk required in the mixture may range from none on some occasions to sixty per cent or more. As a general rule, however, for any given installation the proportion will not vary over such wide limits. If the under-stabilized milk is almost stable and the over-stabilized milk is highly over-stable, the amount of the latter required will be quite small, and vice versa.

What is claimed is:

l. The process of producing sterile evaporated milk which consists in sterilizing by heat evaporated milk m'ade up of a mixture of two quantities of milk of approximately the same composition, one of said quantities being of milk having insufficient heat stability to withstand sterilization by heat without coagulation, said process including the steps prior to sterilization of subjecting the other quantity of milk to a heat treatment at a temperature between 250 F. and 300 F. for about two seconds at the higher temperature to a maximum of about four minutes at the lower temperature to give the milk excessive heat stability and lack of body after sterilization by heat, and mixing said quantities in proportions which as determined by empirical tests will produce milk of proper heat stability, said process including the step of evaporating all of said milk prior to said sterilization.

2. The process of producing sterile evaporated milk which consists in heat-treating a quantity of milk at a temperature between 250 F. and 300 F. for about two seconds at the higher temperature to a maximum of about four minutes at the lower temperature to give the milk excessive heat stability and lack of body after sterilization by heat, mixing said quantity of milk with another quantity of milk having insufficient heat stability to withstand sterilization by heat without coagulation, the proportions of said quantities in the mixture being proportions determined by empirical tests to produce milk of proper heat stability, evaporating the mixture, and sterilizing the evaporated milk by heating the same.

1 3. The process of producing sterile evaporated milk which consists in heat-treating a quantity of milk at a temperature between 250 F. and 300 F. for about two seconds at the higher temperature to a maximum of about four minutes at the lower temperature to give the milk excessive heat stability and lack of body after sterilization by heat, evaporating said quantity of milk, mixing the evaporated milk with another quantity of evaporated milk which has insufficient heat stability to withstand sterilization by heat without coagulation, the proportions of said quantities in the mixture being proportions determined by empirical tests to produce milk of proper heat stability, and sterilizing the mixture by heating the same.

4. The process of producing sterile evaporated milk which consists in heat-treating a quantity of evaporated milk at a temperature between 250 F. and 300 F. for about two seconds at the higher temperature to a maximum of about four minutes at the lower temperature to give the milk excessive heat stability and lack of body after sterilization by heat, mixing said heat-treated evaporated milk with another quantity of evaporated milk having insuflicient heat stability to withstand sterilization by heat without coagulation, the proportions of said quantities in the mixture being proportions determined by empirical tests to produce evaporated milk of proper heat stability, and sterilizing the mixture by heating the same.

' SAMUEL R. PARK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 612,561 Dodd Oct. 18, 1898 1,168,823 Nielsen Jan. 18, 1916 1,432,686 Grindrod Oct. 17, 1922 1,710,508 North Apr. 23, 1929 2,282,800 Musher May 12, 1942 2,290,889 Mook July 28, 1942 OTHER REFERENCES Fundamentals of Dairy Science, by the Associates of Rogers, 2d ed. 1935, Reinhold Publishing Corp., pp. 208-209.

Condensed Milk and Milk Powder, by Hunziker, 5th ed. 1935.

Journal of Dairy Science, Jan. 1929, The Relations of Temperature and Time of Forewarm ing of Milk to the Heat Stability of Its Evaporated Product by Deysher, Webb and Holm.

Journal of Dairy Science, Nov. 1928, Heat Coagulation of Evaporated Milk as Affected by Mixing Different Grades of Raw Milk by Webb, p. 4'71.

Journal of Dairy Science, April 1942', The Effect of High Temperature Short-Time Fore- Warming of Milk Upon the Heat Stability of its Evaporated Product, by Webb and Bell, p. 301. 

1. THE PROCESS OF PRODUCING STERILE EVAPORATED MILK WHICH CONSISTS IN STERILIZING BY HEAT EVAPORATED MILK MADE UP TO A MIXTURE OF TWO QUANTITIES OF MILK OF APPROXIMATELY THE SAME COMPOSITION, ONE OF SAID QUANTITIES BEING OF MILK HAVING INSUFFICIENT HEAT STABILITY TO WITHSTAND STERILIZATION BY HEAT WITHOUT COAGULATION, SAID PROCESS INCLUDING THE STEPS PRIOR TO STERILIZATION TO SUBJECTING THE OTHER QUANTITY OF MILK TO A HEAT TREATMENT AT A TEMPERATURE BETWEEN 250* F. AND 300* F. FOR ABOUT TWO SECONDS AT THE HIGHER TEMPERATURE TO A MAXIMUM OF ABOUT FOUR MINUTES AT THE LOWER TEMPERATURE TO GIVE THE MILK EXCESSIVE HEAT STABILITY AND LACK OF BODY AFTER STERILIZATION BY HEAT, AND MIXING SAID QUANTITIES IN PROPORTIONS WHICH AS DETERMINED BY EMPIRICAL TESTS WILL PRODUCE MILK OF PROPER HEAT STABILITY, SAID PROCESS INCLUDING THE STEP OF EVAPORATING ALL OF SAID MILK PRIOR TO SAID STERILIZATION. 